When a photocatalytic material, typically a metal oxide, is exposed to light of energy higher to the band gap, the material is excited, promoting electrons to the conduction band and creating positive holes in the valence band. Electrons and holes can carry out reduction and oxidation reactions for multiple applications; some of them widely known and other not so much, but undoubtedly, all of them related with our daily life and the quality of our future. 

One of the multiple and usual applications of photocatalysis can be found in the environmental remediation; nowadays it is possible the application of an advanced painting in the exterior of a building that eliminates toxic compounds from air. Due to the integration of a photocatalytic material in a painting formulation that can eliminate volatile organic compounds, NO_X, SO₂, and even CO₂. On the other hand, used in interiors, the material can purify the air and eliminate bad odors.

The same working mechanism is applied to the elimination of toxic compounds present in the soil, e.g., pesticides, fertilizers, chlorophenols; and pollutants in wastewater from industrial and domestic effluents; for example, organic dyes, medicaments, organic additives, among others.

Clean water and air are the most important resources to ensure the persistence of humanity, and photocatalysis offers the possibility of removing contaminants and reducing their impact on the environment.

In the field of construction and transport, international companies are applying self-cleaning coatings strategically deposited on windows and exterior sections for preventing the accumulation of dust and breaking down particles over the surfaces for keeping them clean.  These coatings are currently used in houses, buildings, cars, rapid trains, and planes. Moreover, the coatings also exhibit antifogging properties, ensuring a perfect view when using glasses, mirrors, etc; and when they are used in places with poor ventilation, e.g., tunnels, the photocatalytic material can degrade the pollutants produced from fuel combustion that are in higher concentrations in the tunnels.

For medical applications, photocatalytic coatings and solutions are widely commercialized for antibacterial, antiviral, and antifungal activity. Their efficiency has been proved to inactivate E. coli, and even the virus SARS-CoV-2. Face masks with photocatalytic active material have been put in the market. Furthermore, the application of these coatings has been extended to surfaces that are constantly touched by multiple people, for example, in the bus, escalators, doors, etc., preventing the spread of contagious diseases.

Photocatalytic materials are present in lot of medical utilities, e.g., in surgical clothes to avoid bacterial growth, and some studies have shown a favourable effect for wound infections, and to sterilize rooms, instruments, etc. In addition, nanoparticulated photocatalysts can be used in photodynamic therapy to generate, upon illumination, reactive species that can destroy cancerous cells.

The use of photocatalysis has been extended to agriculture, where it has been found that in tolerable doses, a photocatalyst can enhance the germination of seeds and plant growth, which could be a breakthrough to produce aliments for the big world population, and the growth of trees for a good air quality and the reestablishment of the natural equilibrium in the ecosystems.

The role of photocatalysis in clean energy production

The demonstrated effectiveness of photocatalysis in promoting healthier ecosystems and aiding across various sectors sets a promising precedent for its application in energy generation. It underscores the potential of this versatile technology not just in addressing environmental challenges, but also in tackling the critical need for renewable energy sources.

Only with sunlight, water, CO₂, and a photocatalytic material, it is possible to produce hydrogen and a series of carbon-based fuels such as methane, methanol, ethanol, and value-added products, e.g., formaldehyde and formic acid. For this reason, this process is known as artificial photosynthesis, since it emulates natural photosynthesis in the plants that produces carbohydrates and oxygen from sunlight, water, and CO₂.

Though the conversion efficiencies are still limiting, there is an everyday growing list of companies that are investing in research for making possible the production of solar fuels in the world and contribute to the decarbonization and sustainable development.

Current limitations and perspectives

Currently, the goal in photocatalysis for energy applications is to achieve a higher solar to hydrogen efficiency to make possible hydrogen production in a practical scale. At the same time, in CIC energiGUNE, other more consolidated technologies, e.g. electrolysis and thermochemical water splitting, are already being studied for their implementation at a practical scale, as described in previous articles of the blog.

This article delves into how photocatalysis is already shaping our daily lives and how it holds the key to a sustainable, energy-efficient future, emphasizing its significance in the realm of clean energy production. We hope that this information helps to envision this clean future and attracts a higher participation of all the sectors to achieve the goals of sustainable development.